Various models of world timepieces, particularly of analog type, are known in the art, i.e. timepieces that have a dial and an hour marking mechanism designed to allow simultaneous reading of the time in two or more different time zones of the globe.
One common and simple type of timepieces adds to the normal hour and minute rings, typical of classical analog watches, an additional outer ring, with the names of the places representative of each of the time zones into which the globe is typically divided marked thereon. The name of the place may be combined with an indication of the time offset from the time zone of the user.
Nevertheless, in these solutions the user is forced to calculate the time for each desired time zone from the time indicated by the hands, and while this calculation is simple, it still causes reading of the various time zones non immediate and susceptible to errors.
In other types of timepieces the rings and the hands move relative to each other in a direction opposite to classical dials, with the former being rotatably movable and the latter fixed at a predetermined position, susceptible of being changed by the user.
In certain cases, the hands may be simply replaced by a single fixed reference marked on the dial.
For instance, EP1181625 discloses an analog world timepiece dial, having a central movable disk with the minute division, a first inner ring, also movable, divided into 24 hour sectors, and a fixed index external to both the central minute disk and the hour ring.
The current time is given by the markings of the hours and minutes read from time to time at the fixed index.
The dial also has a second ring, immediately external to the first hour ring, with the names of one or more places for each time zone marked thereon.
Thus, time may be instantly determined for each time zone, by reading the reference numbers of the first ring and the disk, that are aligned with the name of the place representative of the time zone.
While this solution allows substantially simultaneous determination of the time for each time zone, it still has the apparent drawback of having an hour ring divided into 24 sectors, one for each time zone.
Therefore, the dial carries a large amount of information, which causes visual confusion and requires the use of very small characters, both for city names and for reference numbers, thereby preventing easy time reading.
EP0769733 discloses an universal timepiece having a dial with an hour hand a minute hand and an outer city ring with two concentric stripes of markings that indicate location of respective time zones. The markings of the two stripes are arranged to define pair of locations having a respective 12 hours offset local times.
However, the city ring rotates simultaneously with the hour dial, so that the time reading position on the dial changes and the user could not immediately read the time of his proper time zone.